I'm running the live enviroment and trying to edit the tor configuration through the Vidalia GUI results in a "cannot write to disk" error.

I think that option isn't designed for the unix way of dealing with services, like the situation is in Tails, but it will work for the Browser bundles and Windows. In Tails torrc simply isn't writable by the amnesia user, and since vidalia is run by amnesia it cannot modify the file. For this to work you have to temporarily make the file world writeable (or owned by the amnesia user) and the same goes for /etc/tor/.

Editing /etc/tor/torrc as root and restarting the tor process?

I recommend the following:

sudo nano /etc/tor/torrc
sudo service tor reload

Editing /etc/tor/torrc using the sudo command, and then issuing a SIGHUP signal (for example 'sudo service tor reload') does not work anymore in Tails 0.11 although it did work in Tails 0.10.x).

When I attempt to reload the tor configuration file, this is what I get from the Vidalia Message Log:

Notice  Received reload signal (hup). Reloading config and restting internal state.
Notice  Not reloading config file: the controller told us not to.

Vidalia started setting a Tor controller setting called __ReloadTorrcOnSIGHUP to false in version 0.2.16 (Tails 0.11 uses 0.2.17 so we're affected). From the Vidalia changelog:

Sets __ReloadTorrcOnSIGHUP to 0 if SAVECONF failed, which means the
user can't write the torrc file. Fixes bug 4833.

As a workaround you can make temporary (until next tor restart) changes to "torrc" (or really just Tor's internal settings) through Vidalia:

1. In Vidalia, go to "Settings -> Advanced -> Edit current torrc".
2. Make your change in the shown torrc and select your changes.
3. Select "Apply selection only".
4. Uncheck "Save settings".
5. Press ok.

That works except there's no way to remove a parameter / option that you've added. What i mean to say, is that if i add an option to the torrc file that wasn't there originally (using the steps you outlined above), there's no way to remove that option later (using the method you described above).

I guess what i can do is exit vidalia completely (tor is still running), and then just reload the tor config through the command line. I hope it's safe to exit vidalia.